1. Field of the Invention
The present invention relates to novel phosphonium salts and processes for production of and uses for the same.
2. Description of the Related Art
Accounts of Chemical Research, 6, 8-15 (1973) and R. F. Heck, "Palladium Reagents in Organic Syntheses", pp.325-334, Academic Press, N.Y., 1985 describe that 1-substituted-2,7-alkadienes can be synthesized by subjecting a conjugated diene, such as butadiene, isoprene, etc., to telomerization reaction with an active hydrogen compound, such as water, alcohols, carboxylic acids, amines, ammonia, enamines, active methylene compounds, azides, silanes, etc., in the presence of a palladium catalyst and that favorable results can be obtained in the concomitant presence of a ligand such as triphenylphosphine in the reaction system. ##STR2## wherein R is a hydrogen atom or a methyl group; and Y is a group derived from an active hydrogen compound by removal of one active hydrogen atom.
As an example of the production of a 1-substituted-2,7-alkadiene compound by such telomerization reaction, there may be mentioned the production of 2,7-octadien-1-ol by telomerization reaction of butadiene with water as described in U.S. Pat. Nos. 3,670,032, 3,992,456, 4,142,060, 4,356,333 and 4,417,079, for instance.
It is generally acknowledged that in the telomerization reaction of a conjugated diene with an active hydrogen compound in the presence of a palladium catalyst, the use of a tertiary phosphorus compound, such as tri-substituted phosphines or tri-substituted phosphites, as a ligand is not only useful for modulating the reaction rate and reaction selectivity but also instrumental in stabilizing the catalyst. Therefore, as the catalyst for a telomerization reaction, it is common practice to use a low-valence palladium complex containing a ligand, such as a tri-substituted phosphine, or a chemical species prepared by reducing a palladium (II) compound in the presence of a ligand such as a tri-substituted phosphine. However, the following problems are involved in telomerization reactions using such catalysts. (1) The higher the concentration of the ligand, such as a phosphine compound, or the higher the molar ratio of the ligand to palladium, the higher is the stability of the palladium catalyst but the reaction rate is conversely decreased drastically (Chemical Communications, 1971, 330; etc.) and the higher the molar ratio of ligand to palladium, the lower is the selectivity of the reaction to a straight-chain alkadienyl compound, i.e. a compound derived by substitution of one or more active hydrogen atoms of an active hydrogen compound by 2,7-alkadienyl groups (Chemical Communications, 1971, 330; U.S. Pat. No. 3,992,456; etc.). Therefore, it is difficult to reconcile the requirements imposed by these two conflicting tendencies, i.e. stabilization of the palladium catalyst on the one hand and enhancement of high reaction rate and high selectivity to a straight-chain alkadienyl compound on the other hand. (2) The phosphine compound used as a ligand is liable to be oxidized in the presence of palladium [Angewandte Chemie International Edition in English, 6, 92-93, (1967)] and as the phosphine compound is recycled for telomerization reaction over a long time, there occurs an accumulation of its oxidation product, i.e. the phosphine oxide, but this phosphine oxide acts as a catalyst poison to exert adverse effects on telomerization (Japanese Patent Application Laid-Open KOKAI No. 4103/76). Incidentally, the phosphine oxide is hard to be separated and removed. (3) The research of the present inventors revealed that when a telomerization reaction is carried out using an excess of a phosphine compound relative to palladium, even if a low-valence palladium complex prepared from a palladium compound and a phosphine compound, the so-called active catalyst species, is used, the reaction involves a prolonged induction time. Particularly where the telomerization reaction is continuously conducted over a long period of time, more than a necessary amount of the palladium catalyst must be added, for the added catalyst cannot immediately exhibit its activity.
Since palladium is an expensive noble metal, it must be ensured in the use of a palladium catalyst in commercial production that the productivity per unit quantity of palladium be sufficiently high and the catalytic activity be sustained over a long time. From this point of view, it is of utmost importance to solve the aforesaid problems (1) to (3).